1. Field of the Invention
The present invention relates to a mobile communication system. More particularly, the present invention relates to a method and apparatus for setting up a voice call during a Circuit Switched Fallback (CSFB) service.
2. Description of the Related Art
Mobile communication systems have been developed to provide voice services while ensuring a user's activity. However, the mobile communication systems have extended their coverage to include data services beyond the voice services. At present, the mobile communication systems have been developed to be able to provide high-speed data services as well. However, mobile communication systems according to the related art suffer a lack of resources and user demand for higher-speed services continually increases. Thus, further advanced wireless communication systems are required.
To meet the demands for advanced wireless communication systems, the 3rd Generation Partnership Project (3GPP) has been proceeding with standardization for a Long Term Evolution (LTE) communication system as one of the next-generation communication systems under development. The LTE system generally supports only packet services. Hence, the LTE standard proposes a Circuit Switched Fallback (CSFB) service to provide voice calls to users.
FIG. 1 illustrates configuration of a general system that uses a CSFB function according to the related art.
Referring to FIG. 1, the CSFB service refers to a service, in which if a voice call occurs for a User Equipment (UE) 150 that camps on an LTE system 130 connected to an Evolved Packet Core (EPC) 110, the UE 150 is handed over to an existing 2G/3G legacy system 120 so as to be connected to the voice call. The EPC 110 and the existing 2G/3G legacy system 120 are operatively connected to a Mobile Switching Center (MSC) 100.
According to the CSFB process, the UE 150 may perform handover from the LTE system 130 to the 2G/3G legacy system 120 as illustrated in FIG. 1. In order for the UE 150 to have access to the 2G/3G legacy system 120, the UE 150 must receive system information from the 2G/3G legacy system 120. The system information may be divided into multiple blocks depending on the contents included therein, and each System Information Block (SIB) is repeatedly broadcasted at intervals of a few milliseconds to a few seconds depending on the system settings.
As described above, in order for the UE 150 to access the 2G/3G legacy system 120, the UE 150 must receive system information from the 2G/3G legacy system 120 at regular intervals, thereby causing significant degradation of the Quality of Service (QoS) that the UE 150 experiences. In contrast to the process for setting up a voice call directly in the existing 2G/3G legacy system 120, setting up a voice call using CSFB requires an additional process of switching from the LTE system 130 to the 2G/3G legacy system 120 and receiving system information from the 2G/3G legacy system 120. As a result of the time required for handling the additional process is longer, the QoS that the UE experiences may degrade more significantly.
Therefore, a need exists for a method and apparatus for reducing the time required to set up a voice call in an environment in which CSFB is used.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.